What is dark cost?

Excuse me, could you please explain what exactly is meant by "dark cost" in the context of cryptocurrency and finance? I've come across this term a few times but haven't quite been able to grasp its full meaning. Is it related to hidden fees or expenses that investors might encounter while trading digital assets? And if so, how significant can these costs be and what measures can traders take to mitigate them? I'd really appreciate it if you could provide some clarity on this topic.